Internal combustion engines having a cast aluminum block may be manufactured with cast iron liners that provide a durable wear surface that is contacted by the engine's pistons and rings. Liners for 4 to 8 cylinders add substantial weight to the engine that reduces fuel economy.
Thermal spray processes are used to provide a hard smooth surface on a base material. Both cylindrical surfaces, such as cylinder walls of combustion engines, and flat surfaces, such as brake discs, may be provided with a thermal spray coating. Surface preparations are required to provide adequate long term adhesion between the base material and the thermally sprayed surface. Creation of undercuts in this application typically involves use of tooling with multiple inserts with very fine features. Tooling to produce these undercuts is generally characterized by high cost and/or short life.
Preparing a surface to receive a thermal spray coating is problematic and costly. The surface receiving the thermal spray coating must be roughened, typically by grit blasting or by being specially machined to create continuous undercuts along the length of very small grooves. Tool wear for specialized broaching or machining tools requires frequent tool replacement. Additional process steps and removing machining chips and debris adds to the cost of the process and, if the surface is not properly prepared, imperfections may be created that may reduce adhesion of the thermal spray coating that can cause scrap or reduced coating life.
Another method of ensuring adhesion is to use flux or application of a chemical bond coat prior to applying the thermal spray material. Chemical bonding and fluxing preparations add to the cost of manufacturing and may involve the use of hazardous materials.
The method of preparing a surface to receive a thermal spray coating and the structure of the surface prepared and coated with the thermal spray developed by applicants are directed to solving the above problems and other problems relating to surface preparations will be apparent to those of ordinary skill in the art. The solutions proposed by applicants are summarized below.